IPA: /ˈɛr.ər.ləs/
KK: /ˈɛrərləs/
Without any mistakes; completely accurate and correct.
The errorless report impressed the manager with its precision.
Errorless → It is formed from "error" (from Latin "error", meaning a wandering or mistake) and "-less" (meaning without). The word "errorless" means without error or free from mistakes.
Think of being 'without' ('-less') any 'mistakes' ('error') — that's what errorless means.